1. Field of the Invention
The present invention concerns a network of switches having N input ports and T output ports adapted to connect mutually and individually any P from N inputs and any P from T outputs (P.ltoreq.N and P.ltoreq.T).
By resetting the switches the choice of the P inputs or the P outputs can be modified.
This rearrangement must be done with minimum disturbance, i.e. causing as few as possible modifications of existing connections, whilst ensuring that the connections set up pass through the fewest possible switches.
The terms input and output as just used are naturally interchangeable from the point of view of the switch network, with the result that this discussion can be limited to the case T&gt;N.
2. Description of the Prior Art
Networks of this kind are used in telecommunication satellites to set up P simultaneous communication channels chosen by the operator from N possible channels and connecting them individually to P from T equipments of the same type.
They guard against failure of these equipments (T-P equipments maximum), for example. Two symmetrical networks are usually employed, one on each side of the equipments, and their switches are operated simultaneously.
This arrangement enables each of the P (from N) inputs to be connected to one of the P (from T) equipments, which equipment is then connected to one of T inputs of the symmetrical network, which connects it to an output having the same position as the input of the first network.
The switches used in these networks have four poles and connect a first pole to a second, third or fourth pole and correspondingly connect said third pole to said fourth, first or second pole. Using arbitrarily assigned pole numbers:
a three-position switch connects a first pole to a second and a third to a fourth, or a first pole to a third and a second to a fourth, or a first to a fourth and a second to a third; PA1 a four-position switch connects a first pole to a second and a third to a fourth, or a first to a third, or a first to a fourth and a second to a third, or (in the last position) a second to a fourth.
Known network structures are of two types, namely linear (or chain) and ring structures.
The linear or chain structure is used when N=P and T=P+1 or T=P+2. Each switch is connected to its two neighbours except for the two switches at the ends which are connected to the remainder of the network by a single pole. The other available poles of the intermediate switches are respectively assigned to an input and an output. The three available poles of the two switches at the ends of the network are connected one to an input and the other(s) either to a single output, one pole remaining uncommitted, or to two outputs.
The ring structure used in the other cases comprises a main loop comprising all of the switches connected together by two of their poles, each of the other two poles being connected to an input, to an output or to another switch of the ring by a direct link.
These structures have many limitations. They require a high number of switches to implement their function, the rearrangements usually cause extensive modifications to connections already set up, and the number of switches through which the signal passes can then be high.
An object of the present invention is a network having the functions defined above and using the same types of four-pole switches which does not suffer from the drawbacks of known networks.